52 AIR AND FIRE 



Respiration consists both of breathing, which is performed 

 for the higher animals by lungs (cf. 343), and also of the 

 actual oxidation that takes place throughout the body. 

 A grown man takes in ("inspires") about 350 cubic feet 

 (10 cubic meters) of air in a day. 



The purpose of respiration is to get the oxygen of the 

 air to combine with the materials of the body that are 

 constantly wearing out, and to oxidize them (cf. 48) to 

 substances that the body can get rid of. Since this worn- 

 out matter, like the body itself, is largely made up of 

 carbon and hydrogen, it is changed chiefly to carbon 

 dioxide and water when oxidized (cf. 51 and 105). The 

 oxidation within the body is not an actual burning; but 

 it produces heat. This heat keeps the bodies of animals 

 warm. In man the normal temperature is 98.6 Fahren- 

 heit, or 37 Centigrade (cf. 63). In certain diseases the 

 lungs are not able to get oxygen rapidly enough from the 

 air; so pure oxygen is used. 



Water animals depend upon the oxygen dissolved in 

 natural water. Fishes, clams, etc., take in oxygen through 

 their gills (cf. 337 and 341). In the gills the same ex- 

 change of carbon dioxide for oxygen takes place as in the 

 lungs of higher animals. 



53. Exercises. 



1. How can you show that the expired breath contains water? 

 Carbon dioxide? 



2. Give the dates of the birth and the death of Priestley and of 

 Lavoisier. What did each do for science? (See Glossary.) 



3. What substance is used to polish stoves (cf. 119)? How does 

 it prevent rusting? What other materials are used to cover iron to 

 prevent rusting? 



